1. Field of the Invention
The present invention relates to a system or the like for the detection of a force operating on a metallic V-belt which is used to transmit a power in, for example, a V-belt type stepless transmission.
2. Description of the Related Arts
Such type of metallic V-belt is hitherto known, and disclosed in, for example, Japanese Patent Publication Nos. 55-6783 and 61-54976, and Japanese Utility Model laid-open Publication No. 3-72139. This metallic V-belt comprises endless belt-like supporting straps and a multiplicity of metallic blocks supported along the straps, and passes around a driving pulley and a driven pulley.
Both the pulleys are capable of controllably varying their V-groove widths to vary winding radii of the V-belt with respect the pulleys, thereby steplessly changing transmission gear ratio.
In the process of design and manufacture of the stepless transmission having such metallic V-belt, it is required to reduce the size and weight of the metallic V-belt while ensuring a sufficient strength thereof and to control axial thrust in an optimum manner. This would lead to the necessity for more accurate detection of a force operating on the metallic V-belt during the drive. Under these circumstances, a variety of attempts have been made hitherto for the detection of this operating force.
One of such attempts is to detect a force operating on the belt by using a strain gauge directly attached to a metallic block or the like without imparting any machining to the metallic block, the strain gauge being connected to the outside by way of wires for the retrieval of signals. More specifically, "Axial Thrust Operating on New CVT Belt and its Distribution" by Tsunashima and others in Spring Academic Lecture Meeting at Corporation Aggregate Automobile Technical Society (May 24, 1988), for example, discloses a measurement of a force in the direction of axial thrust.
In this case, however, the metallic block is used as it stands without imparting any machining thereto for the thrust measurement, which may result in an insufficient accuracy of resultant values. Moreover, the arrangement in which the detection values of the strain gauge attached to the metallic block are led to the exterior device by way of wires may place a restriction on the rotational speed and accumulative number of rotation, which may adversely lead to a measurement permissible only under extremely low-speed driving conditions.
While on the contrary, an attempt to machine the pulleys for the detection of an operating force is disclosed in an article "Study on Transmitting Characteristics of Block Type CVT belt" published by Kusana or others in Autumn Academic Lecture Meeting at Corporation Aggregate Automobile Technical Society (October, 1991), which involves a problem that the measurable transmission gear ratios are limited to a specific range due to its mechanical construction.
Another attempt to lead the measurement signals produced by the strain gauge attached to the endless belt strap to the outside has been made in, for example, "Behavior Analysis on CVT Belt" (Academic Lecture Meeting Preprint 891, 1989-5) announced by Katsuya or others (Nihon Hatsujyo) in Spring Academic Lecture Meeting at Automobile Technical Society (1989), which entails a problem that the driving conditions are limited to the extremely low speed due to a difficulty in signal transmission from the strain gauge to the outside.
A further attempt is to lead the measurement signals produced by the strain gauge attached to the endless belt strap to the outside by making use of a slip ring for the detection of pulling force of the strap, which is disclosed in, for example, "Load Stress Measurement on CVT Steel Ring" published by Okawa and others (Toyota Jidosya) in Lecture Meeting Articles Vol.C at 69th Ordinary Session in Japanese Machinery Society. This involves a problem that there exists a restriction on the driving conditions such as rotational speed since the signals are transmitted by wires between the strap and the slip ring.
"Maximum Stress Measurement on CVT Steel Ring Using Acoustic Emission" by Ozawa and others (Fuji Jyukogyo Kabushiki Kaisya) published as an article at Automobile Technical Society, 1987. discloses a method of measurement utilizing the acoustic emission, which is less restrictive in the driving conditions at the time of measurement.
Disadvantageously, this method is not suitable for the successive measurement of stress under various driving conditions although it is capable of detecting whether the stress has reached a predetermined value or not.